A mild and concise approach for the construction of 3,4-dihydro-2H-pyran ring integrated into the A-ring of the natural product oridonin using an optimized inverse electron demand hetero-Diels-Alder (IED HDA) reaction is reported herein. A thermal-driven self-dimerization of the exocyclic enone installed in the A-ring through homo-HDA reaction was identified to exclusively give a dimeric ent-kaurane diterpenoid with the spirochroman core. Additionally, the efficient cross-HDA cycloadditions of this enone with various vinyl ethers or vinyl sulfides, instead of its own homo-HDA dimerization, were achieved in regio- and stereoselective manners, thus providing new dihydropyran-fused oridonin derivatives. Further functionalizations of the synthesized dihydropyran rings allow access to two valuable versatile building blocks for advanced structural diversity.

<i>ent-</i>Kaurane-based regio- and stereoselective inverse electron demand hetero-Diels-Alder reactions: Synthesis of dihydropyran-fused oridonin derivatives

247th National Meeting (2014)

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ent-Kaurane-based regio- and stereoselective inverse electron demand hetero-Diels-Alder reactions: Synthesis of dihydropyran-fused oridonin derivatives